The present invention relates to a semiconductor element in which a bump is formed on an electrode of the semiconductor element by a ball bonding method or the like using a metal thin wire (wire), that is, a method of forming a bump electrode on an IC electrode, a method of fabricating the semiconductor element, a semiconductor device fabricated with the semiconductor element and a method of fabricating the semiconductor device.
In recent years, electronic equipment has been developed to have a compact size, a light weight and a high function, and this has also required electronic components to have a compact size, a light weight and a high function. From this point of view, in regard to a method of forming a bump electrode on an IC electrode relevant to the present invention, a mounting method by means of a wire bonding technique is used.
The method of forming a bump electrode on an IC electrode by the aforementioned prior art wire bonding technique will be described below with reference to the drawings.
FIGS. 17A—17D show schematic views of a prior art bump electrode forming method. In the figure are shown an Au wire 101, an Au ball 102, a bonding capillary 103, an IC electrode 104 on a board 170, a ball bond portion 105 and a bump electrode 106.
The method of forming the bump electrode on the IC electrode will be described next.
In FIG. 17A, the Au ball 102 formed at the tip end of the Au wire 101 is supplied onto the IC electrode 104 as shown in FIG. 17B and bonded onto the IC electrode 104 by the bonding capillary 103. Subsequently, the bonding capillary 103 is moved upward, sideway and then downward, thereby connecting the Au wire to the ball bond portion 105 as shown in FIG. 17C. Subsequently, the capillary 103 is moved upward and the Au wire 101 is cut, thereby forming a bump electrode as shown in FIG. 17D.
The above operation will now be described in greater detail. A method of forming a bump on a semiconductor element by a prior art ball bonding method and a method of connecting the semiconductor element provided with the bump are disclosed in U.S. Pat. No. 4,661,192. The methods will be described.
As shown in FIG. 18A, a high voltage of several thousand volts is applied from a torch 160 which serves as a discharge electrode to the tip end 101a of a wire 101 protruding from the tip end 103a of a capillary 103. By the application of this high voltage, the wire 101 is increased in temperature and melted from the tip end 101a while a discharge current is flowing between the torch 160 and the wire tip end 101a, so that a ball-shaped melted portion as shown in FIG. 18B is formed. After the ball 102 is formed, the capillary 103 is moved down to the semiconductor element side, so that the ball 102 is made to abut against an electrode 104 of the semiconductor element 170. By further moving the capillary 103 downwardly with respect to the ball 102 that has abutted against the electrode 104, the ball 102 is bonded to the electrode 104 and the ball 102 is formed by the tip end portion 103a of the capillary 103, so that a bump base portion 8 as shown in FIG. 18C is formed. Next, as shown in FIG. 18D, by moving the capillary 103 upwardly away from the semiconductor element while clamping the wire 101 by means of the capillary 103, the wire 101 is torn off in the vicinity of the bump base portion 8, thereby forming a bump 30 on the electrode 104 of the semiconductor element 170. Consequently, a protruding portion 30a is formed upright on the bump base portion 8 of the bump 30 as shown in FIG. 18D.
In the semiconductor element 170 where the bump 30 is thus formed on the electrode 104, as shown in FIG. 19A, the bump 30 is pressed against a base material 21 on which a flat surface 21a is formed, so that a bump 31 having a flat surface 31a formed by flattening the protruding portion 30a is formed. Subsequently, as shown in FIG. 19B, the bump 31 having the flat surface 31a is brought in contact with a conductive adhesive 18 formed on a stage 41, thereby transferring the conductive adhesive 18 onto the flat surface 31a of the bump 31 and its periphery. Subsequently, as shown in FIG. 19C, by aligning in position the bump 31, onto which the conductive adhesive 18 has been transferred, with an electrode 20 on a circuit board 19 and thereafter making the bump 31 abut against the electrode 20, the bump 31 is bonded to the electrode 20 for the achievement of electrical connection between the semiconductor element 170 and the circuit board 19.
However, according to the bump electrode forming method as described above, the Au wire 101 comes in contact with the IC electrode portion 104 when the Au wire 101 is cut by the capillary 103. Consequently, as shown in FIGS. 20A and 20B, the electrode 106a, 106b exhibits an abnormal shape and an IC electrode material adheres to the tip end of the Au wire 101, causing the issue that the Au ball 102a cannot be normally formed, as shown in FIG. 20C.